As an introduction to the critical subject of psychotherapy, the author briefly presents the features of the currently unfolding paradigmatic change in the field of human health. The new definition of health as a state of physical, psychological and social wellbeing invites us to fill a great void of knowledge in the domain of health, which is now identified as a positive state and no longer as the absence of disease. Although fascinating, the aim to move from the disease model to the complementary (and not alternative) health model is fraught with difficulties. While in the disease domain a broad variety of mental disorders have been investigated and classified, there is a great lack of knowledge concerning the positive dimensions of health. At variance with the disease model, the author underscores that there is no plural form of the word health in our vocabulary. After a brief description of the recent literature, the present article focuses on the intrinsic and specific connection between theory and application. Working in the area of positive health entails a process of promoting human strengths, which is quite different from that involved in fighting illness. It is, therefore, crucial for psychologists to reflect on the topic of psychotherapy and on its use in fostering health. This topic is even more exciting and complex when we pass from a continuum that goes from disease to health to a bi-dimensional view in which disease and health, rather than being viewed as static and separate dimensions, are involved in a dynamic process of interdependence.